1. Field of the Invention
The present invention relates to an electronic still camera, and more particularly to an electronic still camera which converts a still picture of an object by an image pickup element into a color video signal and records the signal.
2. Description of the Prior Art
FIG. 1 is a schematic block diagram showing structure of the conventional electronic still camera, in which an image pickup element 1 photoelectrically converts a still image of an object so as to output a color video signal, and a camera tube or a solid state image pickup element is used for the image pickup element 1. The outputted color video signal of the image pickup element 1 is given to a signal processing circuit 2 and subjected to various signal processings (for example, separation of a luminance signal and a chrominance signal). The output signal of the signal processing circuit 2 is given to an NTSC (National Television System Committee) signal processing circuit 3 and converted into an NTSC system composite TV signal. The output signal of the NTSC signal processing circuit 3 is given to a recording device 4, such as a floppy disc drive unit, and recorded therein. The output signal of the NTSC signal processing circuit 3 is also given to an output terminal 5 and outputted therefrom to an external equipment (for example, a monitor TV or a printer). A timing generator 6 controls operations of the image pickup element 1, signal processing circuit 2, NTSC signal processing circuit 3 and recording device 4. In detail, the timing generator 6 controls the image pickup element 1 to be driven at the synchronous speed defined by the NTSC system, and outputs a clamp pulse and a synchronizing signal to the signal processing circuit 2, the synchronizing signal to the NTSC signal processing circuit 3, and a synchronizing control signal to the recording device 4.
Since the conventional electronic signal camera, as above-mentioned, is controlled by the timing generator 6 of the operation speeds of the entire circuits to comply with the synchronous speed defined by the NTSC system, it has been difficult to satisfy both high resolution and low noise requirements. In other words, it is difficult that both the functions of observing the image pickup result by a monitor TV and of printing it by a printer are satisfied together. Next, the reason for this will be described. First, from the viewpoint of high resolution (especially required at the printer), the number of vertical scanning lines is restricted by the NTSC system, thereby creating a problem that the vertical resolution, when printed, deteriorates. Similarly, as to the horizontal resolution, the NTSC system is limited (to about 350 TV lines) and more resolution can not be desired. On the other hand, in order to improve the horizontal resolution as much as possible, the number of picture elements of theh image pickup element 1 needs to be increased and the horizontal read-out frequency thereof needs to be high, and therefore it is required that the image pickup element 1 and signal processing circuit 2 are designed to have a high frequency characteristic. However, when they are of high frequency, the color video signal is deteriorated, or power consumption increases.